Flexible electrically conductive nanotube sensor for elastomeric devices

ABSTRACT

A flexible substrate has a major surface and a sensor attached to and aligned with the major surface of the substrate. The sensor may have an elastic body containing conductive nanotubes homogeneously distributed therein to form a conductive path and at least two electrodes in electrical connection with the conductive path. Balloons and flexible elements used in medical procedures are particularly useful.

RELATED APPLICATIONS DATA

This application is a Continuation of U.S. patent application Ser. No.13/399,935, filed Aug. 30, 2012, which is in turn a Continuation-in-Partapplication of and claim priority under 35 USC 120 from U.S. patentapplication Ser. No. 13/397,737 filed Feb. 16, 2012.

BACKGROUND OF THE INVENTION Field of Invention

The present invention relates to the field of sensors, particularlysensors that indicate local changes in conditions in or on articles, andmore particularly in the field of positionable sensors that can beapplied to a surface, embedded in or constructed within a device whichexpands or flexes under pressure. The invention also relates to flexibleelectrical sensors for use in various technologies including at lestmedical applications to provide information or measurement on thestress, elongation, pressure, or load that is applied to or placed uponthe sensor. The present invention may be used as part of a device orsystem to provide information or measurement of stress, elongation,pressure, or load in the expansion of the device even in medical fields.In particular, the flexible nanotube composite sensor is bonded to ormolded within an expandable and/or flexible elastomeric medical devicesystem, such as a balloon (such as those delivered through catheters),to measure the performance of the device.

SUMMARY OF THE INVENTION

A flexible element (e.g., film, coating, patch or strip) of elastomericpolymer containing from 0.02 to 8% by total weight of conductivenanotubes provides a useful piezoresistive sensor. These sensors areattached to surfaces of or molded within the expandable or flexibleelastomeric device, and measurements may be taken of changes inresistivity through or across the device (e.g., by measuring low voltagecurrent across the strip) to determine changes in dimensions, stress andpressure on the strip. By having secure attachment to the surface of theexpandable device or having it molded within the expandable device,changes in the dimensions, pressure and stress on the device may beestimated with a significant degree of assurance of meaningful results.

BRIEF DESCRIPTION OF THE FIGURES

FIG. 1 is a table showing a graphic representation of date relatingphysical properties of carbon nanotube silicone rubber composites withinthe generic scope of the present invention.

FIG. 2 is a graphic representation showing electrical resistivityproperties of several carbon nanotube silicone rubber composites.

FIG. 3 is a graph showing the Dynamic Mechanical Analysis (DMA) TanDelta (ratio between Storage and Loss Modulus) and nano-DMA testing of acarbon nanotube silicone rubber composite materials as presented in FIG.1.

FIG. 4 graphically shows the piezoresitive response, measured by thechange in current, of a flexible nanotube sensor as the flexibleelastomeric device is inflated, in which the carbon nanotube sensor ismolded.

FIG. 5 graphically shows the piezoresitive response, measured by thechange in current, of the nanotube sensor as it expands along with theflexible elastomeric device and places pressure, up to 10 Newtons, on avery soft rubber material.

FIG. 6 shows an example of embodiment of a sensor within the genericscope of the present invention. FIG. 6 is a side sectional view of anelectrically conductive polymer sensor 1 comprising of nanotubes toconfer electrical properties.

FIG. 7 shows an example of embodiment of a sensor on a surface of aninflatable balloon element within the generic scope of the presentinvention.

FIG. 8 shows an example of embodiment of a sensor on a surface of aninflatable balloon element within the generic scope of the presentinvention.

DETAILED DESCRIPTION OF THE INVENTION

The following definitions and descriptions are useful in understandingthe scope of technology used in the practice of the present technology.

Nanocomposite Definition:

Nanomaterials that combine one or more separate components in order toobtain the best properties of each component (composite). Innanocomposite, nanoparticles (clay, metal, carbon nanotubes) act asfillers in a matrix, usually polymer matrix.

Nanomaterials Definition:

nanomaterials can be defined as materials which have structuredcomponents with at least one dimension less than 100 nm. Materials thathave one dimension in the nanoscale are layers, such as a thin films orsurface coatings. Some of the features on computer chips come in thiscategory. Materials that are nanoscale in two dimensions includenanowires and nanotubes. Materials that are nanoscale in threedimensions are particles, for example precipitates, colloids and quantumdots (tiny particles of semiconductor materials). Nanocrystallinematerials, made up of nanometre-sized grains, also fall into thiscategory. Preferred dimensions for nanotubes are diameters of from 3Angstroms, preferably at least 5 Angstroms, more preferably at least 10Angstroms up to 100 nm, preferably up to 70 nm, more preferably up to 50nm. Preferred ranges of diameters for nanotubes according to the presentinvention are from 0.5 nm to 30 nm.

Nanometer Definition:

One nanometer (nm) is equal to one-billionth of a meter, 10-⁹ m. Atomsare below a nanometer in size, whereas many molecules, including someproteins, range from a nanometer upwards.

Nanoparticle Definition:

Nanoparticles are particles of less than 100 nm in diameter. Thepreferred size range for diameters of nanotubes described above tends tobe a preferred range for the largest dimension of nanoparticles also.

Nanotube Definition (Carbon Nanotubes):

Carbon nanotubes (CNTs) were discovered by Sumio Iijima in 1991. Carbonnanotubes are generally fullerene-related structures which consist ofrolled graphene sheets, although multiple molecular level structures ofnanotubes and variations in structure have been created and described.There are two generic types of CNT: single-walled (one tube) ormulti-walled (more tubes). Both of these are typically a few nanometersin diameter and several micrometers to centimeters long.

Nanowires Definition:

Nanowires are ultrafine wires or linear arrays of dots, made from a widerange of materials, with nanodimension diameters. These are essentiallyextremely long nanotubes in some instances.

Elastomeric Polymers

Elastomers are usually thermoset resins (requiring crosslinking orvulcanization) but may also be thermoplastic polymers. The polymerchains are cross-linked during curing, i.e., vulcanizing. The molecularstructure of elastomers can be imagined as a ‘spaghetti and meatball’structure, with the meatballs signifying cross-links. The elasticity isderived from the ability of the long chains to reconfigure themselves todistribute an applied stress. The covalent cross-linkages ensure thatthe elastomer will return to its original configuration when the stressis removed. As a result of this extreme flexibility, elastomers canreversibly extend (at least once, and preferably repeatedly withoutinelastic deformation occurring) from 5-700%, depending on the specificmaterial. Without the cross-linkages or with short, uneasilyreconfigured chains, the applied stress would more likely result in apermanent deformation. Temperature effects are also present in thedemonstrated elasticity of a polymer. Elastomers that have cooled to aglassy or crystalline phase will have less mobile chains, andconsequentially less elasticity, than those manipulated at temperatureshigher than the glass transition temperature of the polymer. It is alsopossible for a polymer to exhibit elasticity that is not due to covalentcross-links. For example, crystalline polymers can be treated to altertheir short range versus long range crystalline morphology to alter theelastic properties as well as other physical properties.

Underlying technology within the scope of the present invention includesboth sensors and methods of using sensors in processes or procedures.The novel articles used as sensors in the practice of the presenttechnology comprise millimeter dimension (diameters and or three majordimensions between 0.2 to 100 mm) polymeric structures comprising from0.2% to 8% by total weight of conductive nanotubes. The articles musthave some degree of elastic deformation properties. For example, thearticle should be able to deform (bend, stretch, flex, extend, etc.)such that in at least one dimension (e.g., the length of a nanotube)there can be at least 5% total elastic deformation. That deformationcould be measured from a base line 0 stress article with a return tothat base line 0 stress (unstressed) length that has not inelasticallychanged by more than 0.5%. When used, the articles must have electrodesattached across the conductive dimension of the article, preferablyaligned with the dimension of expected stress and elongation. Althoughthe electrodes may be separated so as to extend perpendicularly oracutely or obtusely with respect to the expected dimension of elongationand stress, the peizoresistive effect is more accurately measured alonga single dimension (or possibly along multiple directions, as thenanotubes often are not uniformly aligned, but may curl and twist intothree dimensional form) parallel with the stress and elongation. Thearticle may have electrodes fixed into the structure or may haveattachment points for attaching the electrodes and placing them intocontact with the conductive layer. The electrodes would extend to and bein electrical communication connection with a current or voltagemeasuring system. A voltage is applied across the conductive layer (thepolymer-containing nanotubes) in the sensor, which may again be parallelwith, perpendicular to or angled with respect to at least one dimensionalong which stress and elongation is expected during use, and thechanges in the current (and/or voltage) is measured and the changes arecorrelated to stress and/or percentages of elongation in the article. Asthe current passed between sensors will change in a repeatable manner nomatter what the orientation between the current flow and theelongation/pressure may be, a look-up table or other correspondencebetween the elongation/strain/pressure and changes in current can beestablished as a reference.

The flexible, elastic and/or expandable article, such as a strip orpatch, may be secured to a surface or molded within an expandableelastomeric device that is to be manipulated or mechanically processedor chemically processed, where such processing or handling hassurrounding concerns about changes in stress, dimensions, pressure orthe like that can be measured by piezoresistive measurements. Anelongate element, such as a sensor tube for example, may be a conductivenanotube-containing polymer of from 0.2 to 10 mm in diameter, and from 2to 100 mm in length. A patch may comprise a square or rectangular ORoval or other geometric shape flat material comprising a conductivenanotube-containing polymer and two opposed edges. The electrodes arepositioned at or about the opposed edges, the current is passed throughthe polymer, stress is applied to the patch, and the change in currentis measured and correlated with amounts of stress and/or dimensionalchanges.

Various aspects of the invention include a piezoresistive sensor havingan electrically conductive elastic body having at least one pair ofopposed ends, and the elastic body containing conductive nanotubeshomogeneously distributed therein, the elastic body having at least onesurface with physical attaching elements thereon and the elastic bodyhaving electrodes attached at each of the at opposed ends. Theconductive elastic body (that is the actual body of the sensor made froma composition) has an elastic range of between about 5% elongation andabout 500% elongation. The conductive elastic body may have for example,from about 0.02% to 8% by total weight of the elastic body (notincluding electrodes) of conductive nanotubes. Preferably the conductivenanotubes are from about 0.2 to 5% by total weight of the conductiveelastic body. The conductive nanotubes may be carbon nanotubes. Theelastic body may be a polymer as described herein. The polymer may, byway of non-limiting examples, be selected from the group consisting ofepoxy resins, silicone resins, ethylenically unsaturated elastomericresins, and natural rubbers. The physical attaching elements areselected from the group consisting of polymers, chemical adhesives,adhesive tapes or mechanical attachments.

The present technology also includes a method of sensing dimensionalchanges, stress changes or pressure changes on a substrate includingsteps (not necessarily in the following order) of: non-destructivelyattaching a piezoresistant sensor to a surface of the device or moldingthe piezoresistant sensor within the device, the piezoresistant sensorcomprising an electrically conductive elastic body having at least onepair of opposed ends, and the elastic body containing conductivenanotubes homogeneously distributed therein, the elastic body having atleast one surface with two opposed ends and electrodes at each of theopposed ends, passing a current through the elastic body between the twoelectrodes, sensing the current passing through the elastic body,performing a mechanical step on the substrate, and measuring changes inthe current between the electrodes. The measured changes are identifiedby an electronic look-up table or other execution of software by aprocessor receiving information/signals of the changes to identifychanges in properties or conditions that are being monitored. Theinformation may then be displayed on a video monitor if desired. Themeasured changes in current between the electrodes is related byexecution of code in a processor to a pressure, stress level or changein dimension during performing of the expansion of the device mechanicalstep.

The invention also relates to a flexible electrically sensor for use inany inflatable or flexible device on which stress or dimensional changesare to be determined, by way of non-limiting examples, tubes, balloonsor coronary, vascular, orthopedic, and pelvic health applications anddevices to provide information or measurement on the stress, elongation,pressure, or load that is applied to a expandable balloon medical deviceduring, for example, a medical procedure or long term retention withinthe body.

The present invention may be described as a flexible substrate having amajor surface and a sensor attached to and aligned with the majorsurface of the substrate, wherein:

the sensor comprises an elastic body containing conductive nanotubeshomogeneously distributed therein to form a conductive path and twoelectrodes in electrical connection with the conductive path. At leasttwo electrodes of the sensor may be in communication with both a powersource and a processor. The sensor may be adhered to the major surfaceor embedded in the major surface. The major surface is preferablynon-conductive. The major surface may comprise an elastomericcomposition having a first modulus of elasticity and the elastic body ofthe sensor has a second modulus of elasticity and wherein the firstmodulus of elasticity is within 40% of the second modulus of elasticity.The major surface may be on an inflatable balloon having a conduit fortransporting fluid into a cavity of the balloon to alter stress on themajor surface of the inflatable balloon. The substrate may operatewherein presence of a nominally maximum fluid volume within the cavitymaintains at least a 0.01 mm/m extension of a dimension in the elasticbody of the sensor. The substrate may have the two electrodes of thesensor in communication with both a power source and a processor. Thesensor may comprise an elastic body of a silicone rubber containing aloading of between 0.5% and 3%, by total weight of conductive nanotubes.The substrate may have the major surface as part of an inflatableballoon having a conduit for transporting fluid into a cavity of theballoon to alter stress on the major surface of the inflatable balloon.The substrate may be part of the major surface which is in turn anelastomeric composition having a first modulus of elasticity and theelastic body of the sensor has a second modulus of elasticity andwherein the first modulus of elasticity is within 40% or within 35% orpreferably within 25% of the second modulus of elasticity. The majorsurface may be on an inflatable balloon having a conduit fortransporting fluid into a cavity of the balloon to alter stress on themajor surface of the inflatable balloon. The major surface may be on anexpandable balloon element in a medical device that applies localizedpressure in a patient. The sensor may comprise an electricallyconductive silicone rubber composite comprised of a liquid siliconerubber with a multi-wall carbon nanotube loading of between 1%-3% byweight and a hardness between 10 and 60 Asker C hardness.

The invention may also include a method of detecting stress, pressure ordimensional changes within an environment comprising positioning withinthe environment a substrate having a major surface and a sensor attachedto and aligned with the major surface of the substrate, the sensorcomprises an elastic body containing conductive nanotubes homogeneouslydistributed therein to form a conductive path and at least twoelectrodes in electrical connection with the conductive path;

-   -   applying a current across the sensor through one of the at least        two electrodes;    -   determining changes in the current; and    -   providing signals indicating changes in the current to a        processor; and    -   the processor executing code to correlate determined changes in        the current to stress, pressure or dimensional changes in the        sensor. These methods may use the substrates, sensors, devices        and compositions described herein.

The composition of the balloon may be biocompatible or non-biocompatibleelastomeric material. Exemplary of the biocompatible polymer materialused in forming the balloons, the links or the stress concentratorsincludes the group of polymers consisting of polyurethanes,polyetherurethanes, polyesterurethanes, silicone, thermoplasticelastomer (C-flex), polyether-amide thermoplastic elastomer (Pebax),fluoroelastomers, fluorosilicone elastomer, styrene-butadiene rubber,butadiene-styrene rubber, polyisoprene, neoprene (polychloroprene),polyether-ether-ketone (PEEK), ethylene-propylene elastomer,chlorosulfonated polyethylene elastomer, butyl rubber, polysulfideelastomer, polyacrylate elastomer, nitrile rubber, a family ofelastomers composed of styrene, ethylene, propylene, aliphaticpolycarbonate polyurethane, polymers augmented with antioxidants,polymers augmented with image enhancing materials, polymers having aproton (HI) core, polymers augmented with protons (H+), butadiene andisoprene (Kraton) and polyester thermoplastic elastomer (Hytrel),polyethylene, PLA, PGA, and PLGA.

The balloons may be part of devices and treatments for many varieties ofmedical procedures in which balloons or any expandable device is used tocreate pressure, increase volume restrictions, deliver materials, removematerials, stabilize organs, and the like. Non-limiting examples of suchprocedures include at least treatment of vascular occlusions, gastricinsertions, spinal stabilization, aneurism stabilization, drug deliveryimplants, joint stabilization, bone stabilization, organ stabilization,delivery of medical devices, infusion devices, penile implants, bladdercontrol devices, intestinal controls, urethral implants, orthopedicimplants and the like.

The following description of the Figures will further assist in anunderstanding of the present technology.

FIG. 1 is a table showing a graphic representation of date relatingphysical properties of carbon nanotube silicone rubber composites withinthe generic scope of the present invention. The table shows thoseproperties of materials composed of a base-platinum-cured, liquidsilicone composition curable to a rubber, the curable composition loadedwith concentrations of 0.5%, 1% and 2% commercially available multi-wallcarbon nanotubes.

FIG. 2 is a graphic representation showing electrical resistivityproperties of several carbon nanotube silicone rubber composites.Loading of 0.12%, 0.25%, 0.5%, 1.0% and 2.0% of commercially availablemulti-wall carbon nanotubes was added to a standardized composition ofplatinum cured liquid silicone rubber given in FIG. 1. Unless statedotherwise, the standard elastomer used in all examples (for convenienceand to allow facile comparison of results only, a single composition wasused, although not limiting the scope of the invention and presentedwith all data provided herein) was Shin Etsu X-34-1372, a two part,platinum cured liquid silicone rubber. The nanotubes were multiwallcarbon nanotubes manufactured by Hyperion Catalysis and areapproximately 4 nm in diameter by 1 micron or less in length.

The resultant electrical resistivity values, measured in Ohms cm, areplotted. The dramatic drop in electrical resistivity with very lowloadings of carbon nanotubes is evident. The present invention mayincorporate compositions displaying the electrical resistivityproperties shown in FIG. 2 for a nanotube sensor, or other compositions,as generically described herein that display sufficient levels ofresistance and piezoelectric resistivity as described herein.

FIG. 3 is a graph showing the Dynamic Mechanical Analysis (DMA) TanDelta (ratio between Storage and Loss Modulus) and nano-DMA testing of acarbon nanotube silicone rubber composite materials as presented inFIG. 1. The DMA plot is Tan Delta which is a ratio of the storage andloss modulus. Also are plotted a conventional DMA test with the nanoDMAtesting. Dynamic Mechanical Analysis was carried out by Akron Research &Development Labs using a Visco Analyzer 2000 DMA150 in compression mode.Nanomechanical measurements were performed on a Hysitron TI 900Tribolndenter™ tester by Hysitron, Inc. The graphically displayedresults show the relationship between the DMA and the nano-DMAmeasurements of a frequency sweep from 20 to 200 hertz, and indicate acorrelation of dynamic mechanical properties at the micro and nanolevels of performance under strain. The indications are that the lowloadings of carbon nanotubes within the general scope of the presentinvention (e.g., 0.5% to about 3% by total weight of the composition)does not adversely affect the mechanical performance of the materialcompared to the un-filled base material, thus preserving the physicalproperties of the chosen base polymer.

FIG. 4 shows the piezoresitive response, measured by the change incurrent, of a flexible nanotube sensor, composed of material chosenfrom, but not limited to, FIG. 2, as it is stretched as the flexibleelastomeric device is inflated, in which the cnt sensor is molded.

FIG. 5 shows the piezoresitive response, measured by the change incurrent, of the nanotube sensor, composed of material chosen from, butnot limited to, FIG. 2 as it expands along with the flexible elastomericdevice and places pressure, up to 10 Newtons, on a very soft rubbermaterial.

FIG. 6 shows an example of embodiment of a sensor within the genericscope of the present invention. FIG. 6 is a side sectional view of anelectrically conductive polymer sensor 1 comprising of nanotubes toconfer electrical properties. The sensor is comprised of the curedsilicone polymer (or equivalent elastomer or flexible polymer). This isa flexible silicone rubber with carbon nanotube uniformly (essentiallyhomogeneously, within the limits of real physical limits on the use offinite material) dispersed within the polymer at a preferred loading ofbetween 0.5% and 3.0%. On each end of material 1 an electrical wire 2and 4 (electrode) and connection 3 which are molded or affixed to thecarbon nanotube rubber 1. The sensor is molded within the elastomericmedical balloon device, where a medical grade polymer encompasses thesensor. The sensor 601 is shown with its two leads 602 604 attached atpoints 603 embedded within medical grade silicone layers. A secondembodiment is shown with the sensor 601, leads 602 604 and connectionpoints 603 carried within the volume of an inflated balloon.

FIG. 7 shows an example of embodiment of a sensor within the genericscope of the present invention. FIG. 7 is a side sectional view of anelectrically conductive polymer sensor 1 comprising of nanotubes toconfer electrical properties. The sensor is comprised of the curedsilicone polymer (or equivalent elastomer or flexible polymer). This isa flexible silicone rubber with carbon nanotube uniformly (essentiallyhomogeneously, within the limits of real physical limits on the use offinite material) dispersed within the polymer at a preferred loading ofbetween 0.5% and 3.0%. On each end of material 701 an electrical wire702 and 704 (electrode) and connection 703 which are molded or affixedto the carbon nanotube rubber 701. Additionally, for example, betweenelectrical wires 702 and 704 additional wires 705 and 706 may beapplied, and connection 703 the sensor is molded within the elastomericmedical balloon device, where a medical grade polymer encompasses thesensor. The total number of wires connected to conductive polymer 701may be 3 or more. The sensor is molded within the elastomeric medicalballoon device, where a medical grade polymer encompasses the sensor.

FIG. 8 shows examples of embodiment of a sensor within the generic scopeof the present invention. FIG. 8 is a side sectional view of anelectrically conductive polymer sensor 1 comprising of nanotubes toconfer electrical properties. The sensor is comprised of the curedsilicone polymer (or equivalent elastomer or flexible polymer). This isa flexible silicone rubber with carbon nanotube uniformly (essentiallyhomogeneously, within the limits of real physical limits on the use offinite material) dispersed within the polymer at a preferred loading ofbetween 0.5% and 3.0%. On each end of material 801 an electrical wire 2and 4 (electrode) and connection 803 which are molded or affixed to thecarbon nanotube rubber 801. Additionally, for example, betweenelectrical wires 802 and 804 additional wires 805 and 806 may beapplied, and connection 3 the sensor is molded within the elastomericmedical balloon device, where a medical grade polymer encompasses thesensor. The total number of wires connected to conductive polymer 801may be 3 or more. The sensor is affixed to a surface, interior orexterior, of the elastomeric medical balloon device.

To achieve desired or designed electrical properties to a polymer orelastomer as described herein, such as an epoxy resin, elastomericpolymer or rubber, addition of moderate percentages, such as between0.5% up to 4% by total weight of the polymer of conductive nanoparticlesand especially carbon nanoparticles may be used. Loading with largerconductive particles such as carbon black at levels above 10% by totalweight of the composition or total weight of the elastomer, often resultin compromised physical properties such as hardness, tensile, thermaland compression. In addition, the electrical conductivity is negativelyaltered upon large deformations of the material to the point wherebyelectrical contact between the conducting particles is broken. Theaddition of very small amounts, even less than 2% by total weight of thecomposition (as described herein), of carbon nanotubes increases theelectrical conductivity of the base material while preserving desiredphysical properties of the original polymer. The relatively lowerloading of carbon nanotubes to a silicone rubber elastomer preservedesired original liquid silicone rubber physical properties such ashardness, tensile, elongation and compression. Low loading, by weight,of carbon nanotubes to a base polymer significantly changes theelectrical properties. For example, a 0.5% or 1.0% loading of multi-wallcarbon nanotubes dispersed into a liquid polymerizable to a siliconerubber, changes the resistivity of the original silicone rubberelastomer from 10¹³ Ωcm to 10³ Ωcm, with no significant change in theother important properties of the original properties. Additionally,large deformations of the nanotube composite do not negatively affectthe electrical conductance of the material rather the electricalconductivity is maintained.

Also considered within the scope of this disclosure are: types of sensordevices and/or systems used to determine and/or measure strain orpressure. The sensors are used to determine and/or measure the amount ofpressure or strain applied to an associated surface and used todetermine and/or measure tissue thickness, and to determine or measurepressure and/or to provide pressure or strain data to a processor whichcorrelates the pressure data with tissue thickness using a look-up tableor other data structure. By knowing the strain or pressure data, asurgeon or technician can then determine the proper alignment of thedevice before completing the medical procedure.

The processor may be housed in a remotely programmable apparatus whichalso includes a memory for storing the script programs and the responsesto voltage data flow. The remotely programmable apparatus may furtherinclude a microprocessor connected to the wires (effectively thecommunication device from the sensor, with or without a preamplifier), auser interface, and the memory. The microprocessor executes the scriptprograms to identify the strain, communicate the results sets to thepractitioner (e.g., through a monitor or printed output or audiosignal), receive possible responses to the results of the data (e.g., asignal to readjust the device or reduce the exhibited strain), andtransmit the responses to the server and/or monitor throughcommunication networks.

The system may also include wireless communication between the voltagemeter reading sensor output and the processor. For example, amicroprocessor may be preferably connected to memory using a standardtwo-wire I²C interface or using a wireless connection. Themicroprocessor is also connected to user input buttons to initiateactivity, alter read-outs requested, respond to signals from the sensor,start a print-out, and the like (as through an I/O port or dedicatedprinter port, LED, a clock and a display driver. The clock couldindicate the current date and time to the microprocessor and measureduration of strain or pressure. The clock may be a separate component,but is preferably built into microprocessor. The display driver operatesunder the control of microprocessor to display information on a videodisplay or monitor. The microprocessor may be any microprocessor in anyformat, including a laptop (PC or Mac) and operate on any operatingsystem, including Linux. For example, a PIC 16C65 processor whichincludes a universal asynchronous receiver transmitter (UART) is anexample of a useful processor for communicating with a modem and adevice interface. A CMOS switch under the control of the microprocessoralternately connects modem and interface to the UART.

For the purposes of the implementation of the invention, a study wasconducted using very low loadings of carbon nanotubes in an elastomericliquid silicone rubber polymer. The resultant data concluded thatdesirable electrical properties were conferred to the liquid siliconerubber elastomeric polymer with relatively low, e.g., less than 4% orless than 3%, loadings of multi-walled carbon nanotubes. In addition,the study showed that the desired physical properties were maintained,and that no diluent behavior was observed. Further, the study showedthat uniform resistivity was achieved throughout the liquid siliconecarbon nanotube rubber composite. These conclusions support theinference that a liquid silicone carbon nanotube rubber composite can beeffectively designed as an electrically conductive elastomeric material,while maintaining desirable physical properties such as tensilestrength, elongation to break, compression and hardness.

Conventional and nano static and dynamic properties testing ofmaterials, such as tensile, elongation, compression set, DynamicMechanical Analysis, surface and volume resistivity, etc., are oftenused to characterize material properties. Values from these tests areconsidered in the choice of materials suitable for application in theflexible sensor. Such test were conducted on carbon nanotube liquidsilicone rubber composites to evaluate the effect of different loadingsof carbon nanotube with different liquid rubbers. In addition for thepurpose of the invention, a study was conducted using very low loadingof carbon nanotubes in an elastomeric silicone rubber polymer, measuringthe changes in the electrical resistivity of the composite polymerduring deformation. The changes in resistivity were measured as afunction in the change of the output current of the material with aconstant voltage applied to the material. The study compared loadings,by weight, of carbon nanotubes homogeneously mixed in the standardsilicone polymers of between 0.5% and 2%. The resultant composites weredeformed under various loading conditions and the change in resistivityof the composite monitored. For the purpose of the medical application,the study used voltages of between 0.01 and 1 volts. The study conductedmeasured large repeated deformations such as tensile strain in the orderof 10 mm elongation as well as small deformation in the order ofmicrons. The resultant change in resistivity correlated with the amountof deformation or force applied to the polymer composite. Although theterm “constant voltage” is used, other electrical measurements are alsoused. For example, a constant current may be used (and voltage measured)It is also possible to use any other means such as resistive bridgecircuit configurations or ballast circuits to determine resistancechange.

Another aspect of the present technology includes accurate measurementof the amount of deformation of, strain exhibited on, or pressureexerted upon, an elastomeric medical device or component orsub-component inserted into a patient is determined by utilizing asensor as described herein attached to or molded within the elastomericmedical device and exhibiting the above described piezoresitiveproperties that conductive nanotubes confer to an elastic medium. Such asensor can be used to measure elongation or strain of a medical deviceduring insertion, or immediately after insertion or even long afterinsertion into the patient. Such a sensor can also measure thedeformation or load that is placed upon the medical device by the organor with the body part with which the medical device is in contact. Thatmeasurement may be a direct pressure measurement, or by comparing strainwith known degrees of pressure applied perpendicular to the sensor (andusing a look-up table). Such a sensor may also be used to measure theamount of pressure that is being applied to a body part by the medicaldevice. Such a sensor may also be used to monitor changes over time ofthe elongation, deformation, strain, load or pressure of an object orbody part to which the sensor is affixed.

The present invention also relates to an electrically conductive rubberwhereby the conductive agent applied to a flexible polymer base may becarbon nanotubes. The carbon nanotubes loadings are dispersedhomogeneously into the polymer base such that the flexibility of theoriginal base polymer is not dramatically compromised, and such that theelectrical response of the composite is not significantly compromised(e.g., by more than 15%) over repeated deformations (e.g., over 20deformations with greater than 100% elongation). A constant voltage isapplied to the sensor and the electrical current is monitored at a pointsome distance from the voltage input through electrical connection withthe electrodes or wires on the sensor. As the sensor is deformed, thecurrent will change in response to the deformation due to the change inelectrical resistivity of the composite material. For sensingdeformation in devices in medical applications, the input voltage may bevery low, in the order of less than 1 volt (e.g., 0.05 up to 1 volt),depending upon the electrical conductivity of the composite polymer. Formedical applications the nanotube composite may be incased within aflexible polymer to insulate the electrically conductive composite andto comply with FDA regulations that may concern nano particle exposure.

The invention further relates to a sensor for which elongation and/orstress of the sensor is directly related to the distance that thesensor, or the medical device to which the sensor is affixed, is pulled,stressed, flexed, expanded or compressed. The distance may be acontinuous pull, inflated expansion or compression or an incrementalpull, stress, inflated expansion or compression of the sensor. Thechange in resistivity of the nanotube composite sensor directlycorrelates to the change in distance that the sensor is pulled,stressed, flexed or compressed. The change in resistivity may bemeasured directly as a change in resistance or as the change in currentwhen a constant voltage is applied. Additionally, the load placed uponthe sensor, or the medical device to which it is affixed or moldedwithin, can be determined likewise by the change in resistivity of thenanotube composite sensor.

Various other aspects of the invention also relate to a flexibleelectrically conductive nanotube silicone rubber composite that iscontained within a non electrically conductive medical grade siliconerubber, for the express purpose of distance, inflated expansion,compression or load measurement by observing the change in electricallyresistivity of the nanotube composite. The attaching element can be usedto attach the sensor directly to other sensors or devices attached to amedical patient for the purpose of measuring the stress or strain orother applied forces to the device. Additionally a sensor is describedhaving at least an elastic body containing conductive nanotubeshomogeneously distributed therein, the sensor contained or attached toor molded within an elastic body not containing conductive nanotubes andnot electrically conductive, of which at least one surface of the sensorwith physical attaching element thereon. Where embedded in anothermaterial, the attaching members assure elongation along with theembedding body.

Another aspect of the technology includes a sensor comprising of anelastic body comprised of a silicone rubber containing a loading ofbetween 0.5% and 3%, by wt. of conductive nanotubes such as carbonnanotubes, homogeneously distributed therein, with electrodes adhered toor molded within the nanotube composite for the purpose of applying anelectrical current through the composite and a detection system thatdetects absolute amounts of voltage and/or changes in voltage across theelectrodes.

A further aspect of the present technology may include a sensor havingan elastic body comprised of a liquid silicone rubber containing aloading of between 0.5% and 3%, by wt. of carbon nanotubes,homogeneously distributed therein, with electrodes adhered to or moldedwithin the nanotube composite and contained entirely within a medicalgrade non conductive flexible silicone rubber.

Another aspect of the present invention may include an electricallyconductive silicone rubber composite comprised of a liquid siliconerubber with a multi-wall carbon nanotube loading of between 1%-3% byweight and a hardness between 10 and 60 Asker C hardness.

An electrically conductive silicone rubber composite comprised of aliquid silicone rubber with a multi-wall carbon nanotube loading ofbetween 0.5%-3% by weight, a hardness of between 10 and 60 Asker C andelongation property greater than 200%.

An electrically conductive silicone rubber composite comprised of aliquid silicone rubber with a multi-wall carbon nanotube loading ofbetween 1%-3% by weight, a hardness of between 10 and 60 Asker C, anelongation property greater than 200% and electrical resistivity of 10³Ohm/sq or less.

Although specific dimensions, compositions, voltages, materials andfields of use are described herein, it must be understood that these areexamples enabling the generic scope of the invention and should notlimit the scope of enforcement of claims herein.

What is claimed:
 1. A flexible substrate having a major surface and asensor attached to and aligned with the major surface of the substrate,wherein: the sensor comprises an elastic body containing conductivenanotubes homogeneously distributed therein to form a conductive pathand at least two electrodes in electrical connection with the conductivepath; and the major surface comprises an elastomeric composition havinga first modulus of elasticity and the elastic body of the sensor has asecond modulus of elasticity and wherein the first modulus of elasticityis within 40% of the second modulus of elasticity.
 2. The substrate ofclaim 1 wherein the at least two electrodes of the sensor are incommunication with both a power source and a processor.
 3. The substrateof claim 2 wherein the sensor adhered to the major surface or embeddedin the major surface.
 4. The flexible substrate of claim 1 wherein themajor surface is non-conductive.
 5. The substrate of claim 1 wherein themajor surface is on an inflatable device having a conduit fortransporting fluid into a cavity of the inflatable device to alterstress on the major surface of the inflatable device.
 6. The substrateof claim 1 wherein the major surface is on a compressible device havinga conduit for transporting fluid into a cavity of the compressibledevice to alter stress on the major surface of the compressible device.7. The substrate of claim 5 wherein presence of a nominally maximumfluid volume within the cavity maintains at least a 0.01 mm/m extensionof a dimension in the elastic body of the sensor.
 8. The substrate ofclaim 5 wherein the major surface comprises an elastomeric compositionhaving a first modulus of elasticity and the elastic body of the sensorhas a second modulus of elasticity and wherein the first modulus ofelasticity is within 20% of the second modulus of elasticity.
 9. Thesubstrate of claim 5 wherein the two electrodes of the sensor are incommunication with both a power source and a processor.
 10. Thesubstrate of claim 6 wherein the two electrodes of the sensor are incommunication with both a power source and a processor.
 11. Thesubstrate of claim 7 wherein the two electrodes of the sensor are incommunication with both a power source and a processor.
 12. The sensorof claim 1 wherein the sensor comprises an elastic body of a siliconerubber containing a loading of between 0.5% and 3% by total weight ofconductive nanotubes.
 13. The sensor of claim 1 wherein the sensorcomprises an elastic body of a silicone rubber containing a loading ofbetween 0.5% and 3% by total weight of homogeneously dispersedconductive nanotubes forming a conductive path through the elastic body.14. The substrate of claim 13 wherein the major surface is on anextendable device having a conduit for transporting fluid into a cavityof the balloon to alter stress on the major surface of the extendabledevice.
 15. The substrate of claim 14 wherein the major surfacecomprises an elastomeric composition having a first modulus ofelasticity and the elastic body of the sensor has a second modulus ofelasticity and wherein the first modulus of elasticity is within 10% ofthe second modulus of elasticity.
 16. The substrate of claim 1 whereinthe sensor comprises an electrically conductive silicone rubbercomposite comprised of a liquid silicone rubber with a homogeneouslydispersed multi-wall carbon nanotube loading of between 1%-3% by weightand a hardness between 10 and 60 Asker C hardness.
 17. A method ofdetecting stress, pressure or dimensional changes within an environmentcomprising positioning within the environment a substrate having a majorsurface and a sensor attached to and aligned with the major surface ofthe substrate, the sensor comprises an elastic body containingconductive nanotubes homogeneously distributed therein to form aconductive path and at least two electrodes in electrical connectionwith the conductive path; applying a current across the sensor throughone of the at least two electrodes; determining changes in the currentor voltage; and providing signals indicating changes in the current to aprocessor; and the processor executing code to correlate determinedchanges in the current to stress, pressure or dimensional changes in thesensor.
 18. The method of claim 17 wherein the sensor is attached to andaligned with a flexible substrate having a major surface to form adevice, wherein: the sensor comprises an elastic body containingconductive nanotubes homogeneously distributed therein to form aconductive path and at least two electrodes in electrical connectionwith the conductive path; and the major surface comprises an elastomericcomposition having a first modulus of elasticity and the elastic body ofthe sensor has a second modulus of elasticity and wherein the firstmodulus of elasticity is within 40% of the second modulus of elasticity.19. The method of claim 18 wherein the device is attached to tissue of apatient and the current is applied either during or after attachment ofthe device to the tissue.
 20. The method of claim 19 wherein stress isintentionally applied to the device by an operator during or afterattachment of the device to tissue while the current is applied.